Energy storage system for storing energy in a waterbody

Abstract

The invention provides an energy storage system ( 1 ) for storing energy in a waterbody ( 2 ), such as a sea, an ocean, a waterway, etc. The energy storage system comprises a reservoir structure ( 8 A, 8 B, 8 C, 9 A, 9 B, 9 C) for a working liquid ( 7 ) and an energy storing and retrieving subsystem ( 10 A, 10 B). The working liquid ( 7 ) in the reservoir structure is completely separated from the water ( 6 ) of the waterbody. The reservoir structure comprises a deformable pressurizing subreservoir ( 8 A), which is extending in the waterbody, and which has a liquid-impermeable deformable wall structure ( 18 ). The reservoir structure further comprises a buried depressurizing subreservoir ( 9 A), which is an artificial structure, which has been buried under a vertical column of a waterbody underground ( 5 ). The energy storage system provides, inter alia, improved energy storage capacity and improved reliability, as well as reduced operational costs and reduced environmental disturbance.

The invention claimed is: 
     
       1. An energy storage system for storing energy in a waterbody, the waterbody having a water surface and a bottom surface, said bottom surface bounding a waterbody underground under the waterbody, wherein the energy storage system comprises:
 a reservoir structure, which comprises a pressurizing reservoir and a depressurizing reservoir, each of which is configured for holding a working liquid beneath the water surface of the waterbody and separated from water of the waterbody in such manner that the working liquid within the pressurizing reservoir and the depressurizing reservoir and the water of the waterbody cannot mix with one another, wherein:
 at least one deformable pressurizing subreservoir of the pressurizing reservoir is at least partly extending in the waterbody, has a liquid-impermeable deformable wall structure, and is configured for pressurizing the working liquid contained within the pressurizing reservoir by deformation of the deformable wall structure under influence of hydrostatic pressure of the water of the waterbody acting on the deformable wall structure, and 
 the depressurizing reservoir is arranged and configured for shielding the working liquid within the depressurizing reservoir from pressurization under influence of the hydrostatic pressure of the water of the waterbody; 
 
 an energy storing and retrieving subsystem configured for:
 guiding the working liquid to flow from the pressurizing reservoir into the depressurizing reservoir, and vice versa, 
 storing energy by increasing a potential energy of the working liquid within the reservoir structure by displacing part of the working liquid from the depressurizing reservoir into the pressurizing reservoir, thereby causing said at least one deformable pressurizing subreservoir, by said deformation of the deformable wall structure, to expand against the action of said hydrostatic pressure of the water of the waterbody, and 
 retrieving stored energy by decreasing the potential energy of the working liquid within the reservoir structure by releasing part of the working liquid to flow from the pressurizing reservoir into the depressurizing reservoir, thereby causing said at least one deformable pressurizing subreservoir, by said deformation of the deformable wall structure, to collapse under the action of said hydrostatic pressure of the water of the waterbody; 
 wherein at least one buried depressurizing subreservoir of the depressurizing reservoir is an artificial structure, which has been buried under a vertical column of said waterbody underground, wherein said vertical column has a height of at least 5 meters, and 
 wherein said at least one buried depressurizing subreservoir is arranged at least 5 meters lower than said at least one deformable pressurizing subreservoir, which is extending in the waterbody, in the sense that, whereby in operation of the energy storage system, the working liquid inside said at least one buried depressurizing subreservoir is at least 5 meters lower than the working liquid inside said at least one deformable pressurizing subreservoir, 
 
 wherein a horizontal flatness ratio of said at least one buried depressurizing subreservoir is at least 2.0, said horizontal flatness ratio being defined as a quotient having a numerator and a denominator, 
 wherein the numerator is a square root of a surface area of a projection area of a horizontal reference plane, said projection area being obtained by vertically projecting said at least one buried depressurizing subreservoir onto said horizontal reference plane, and 
 wherein the denominator is an overall vertical height of said at least one buried depressurizing subreservoir. 
 
     
     
       2. The energy storage system according to  claim 1 , further comprising a shaft structure, wherein:
 the shaft structure is extending at least from the bottom surface of the waterbody downwards through said waterbody underground, 
 at least one descending pressurizing subreservoir of the pressurizing reservoir is extending in or at the shaft structure and downwards along the shaft structure, and 
 the energy storing and retrieving subsystem is at least partly located in or at the shaft structure such that said displacing part of the working liquid from the depressurizing reservoir into the pressurizing reservoir, and said releasing part of the working liquid to flow from the pressurizing reservoir into the depressurizing reservoir, take place in or at the shaft structure and via said at least one descending pressurizing subreservoir. 
 
     
     
       3. The energy storage system according to  claim 1 , wherein said energy storing and retrieving subsystem comprises at least one pump for said displacing part of the working liquid from the depressurizing reservoir into the pressurizing reservoir. 
     
     
       4. The energy storage system according to  claim 1 , wherein said energy storing and retrieving subsystem comprises at least one turbine for said releasing part of the working liquid to flow from the pressurizing reservoir into the depressurizing reservoir. 
     
     
       5. The energy storage system according to  claim 1 , wherein said energy storing and retrieving subsystem comprises at least one reversible hydroelectric turbine, which can operate both as a turbine-generator and, in reverse, as an electric motor-driven pump, for said displacing part of the working liquid from the depressurizing reservoir into the pressurizing reservoir, as well as for said releasing part of the working liquid to flow from the pressurizing reservoir into the depressurizing reservoir. 
     
     
       6. The energy storage system according to  claim 1 , wherein:
 said vertical column has a height of at least 10 meters, and 
 said at least one buried depressurizing subreservoir is arranged at least 10 meters lower than said at least one deformable pressurizing subreservoir, which is extending in the waterbody, whereby in operation of the energy storage system, the working liquid inside said at least one buried depressurizing subreservoir is at least 10 meters lower than the working liquid inside said at least one deformable pressurizing subreservoir. 
 
     
     
       7. The energy storage system according to  claim 1 , wherein said horizontal flatness ratio of said at least one buried depressurizing subreservoir is at least 4.0. 
     
     
       8. The energy storage system according to  claim 7 , wherein said horizontal flatness ratio of said at least one buried depressurizing subreservoir is at least 8.0. 
     
     
       9. The energy storage system according to  claim 1 , wherein the at least one buried depressurizing subreservoir is buried directly under the waterbody. 
     
     
       10. The energy storage system according to  claim 1 , wherein the depressurizing reservoir is not ventilated relative to an atmospheric outside environment. 
     
     
       11. An energy storage system for storing energy in a waterbody, the waterbody having a water surface and a bottom surface, said bottom surface bounding a waterbody underground under the waterbody, wherein the energy storage system comprises:
 a reservoir structure, which comprises a pressurizing reservoir and a depressurizing reservoir, each of which is configured for holding a working liquid beneath the water surface of the waterbody and separated from water of the waterbody in such manner that the working liquid within the pressurizing reservoir and the depressurizing reservoir and the water of the waterbody cannot mix with one another, wherein: 
 at least one deformable pressurizing subreservoir of the pressurizing reservoir is at least partly extending in the waterbody, has a liquid-impermeable deformable wall structure, and is configured for pressurizing the working liquid contained within the pressurizing reservoir by deformation of the deformable wall structure under influence of hydrostatic pressure of the water of the waterbody acting on the deformable wall structure, and 
 the depressurizing reservoir is arranged and configured for shielding the working liquid within the depressurizing reservoir from pressurization under influence of the hydrostatic pressure of the water of the waterbody; 
 an energy storing and retrieving subsystem configured for: 
 guiding the working liquid to flow from the pressurizing reservoir into the depressurizing reservoir, and vice versa, 
 storing energy by increasing a potential energy of the working liquid within the reservoir structure by displacing part of the working liquid from the depressurizing reservoir into the pressurizing reservoir, thereby causing said at least one deformable pressurizing subreservoir, by said deformation of the deformable wall structure, to expand against the action of said hydrostatic pressure of the water of the waterbody, and 
 retrieving stored energy by decreasing the potential energy of the working liquid within the reservoir structure by releasing part of the working liquid to flow from the pressurizing reservoir into the depressurizing reservoir, thereby causing said at least one deformable pressurizing subreservoir, by said deformation of the deformable wall structure, to collapse under the action of said hydrostatic pressure of the water of the waterbody; 
 wherein at least one buried depressurizing subreservoir of the depressurizing reservoir is an artificial structure, which has been buried under a vertical column of said waterbody underground, wherein said vertical column has a height of at least 5 meters, 
 wherein said at least one buried depressurizing subreservoir is arranged at least 5 meters lower than said at least one deformable pressurizing subreservoir, which is extending in the waterbody, whereby in operation of the energy storage system, the working liquid inside said at least one buried depressurizing subreservoir is at least 5 meters lower than the working liquid inside said at least one deformable pressurizing subreservoir, and 
 wherein an air pressure within the depressurizing reservoir is kept at substantially vacuum pressure level.